PBNZT ferroelectric film, sol-gel solution, film forming method and method for producing ferroelectric film

ABSTRACT

To provide a PBNZT ferroelectric film capable of preventing sufficiently oxygen ion deficiency. The PBNZT ferroelectric film according to an embodiment of the present invention is a ferroelectric film including a perovskite-structured ferroelectric substance represented by ABO 3 , wherein the perovskite-structured ferroelectric substance is a PZT-based ferroelectric substance containing Pb 2+  as A-site ions and containing Zr 4+  and Ti 4+  as B-site ions, and the A-site contains Bi 3+  as A-site compensation ions and the B-site contains Nb 5+  as B-site compensation ions.

TECHNICAL FIELD

The present invention relates to a PBNZT ferroelectric film, a sol-gelsolution, a film forming method using the sol-gel solution, aferroelectric material film formed by the film forming method, and amethod for producing a ferroelectric film.

BACKGROUND ART

(1) A PZT Film by a Sol-Gel Method

A PZT film formed by a sol-gel method is conventionally known. However,the PZT film has following drawbacks.

Since Pb has a high vapor pressure, Pb comes out easily from the PZTfilm. As the result, according to the principle of electric chargeneutrality, an oxygen ion deficiency is large, a leak current density islarger than 10⁻⁶ A/cm², and the film is a porous film containing largeamount of air bubbles, and furthermore, in the case of a thick film of 1μm or more used for MEMS, the film has black color and has lostinterference color. Moreover, in a sol-gel method by spin coating, whena thick PZT film of 1 μm or more is to be fabricated, cracks appeareasily due to a large residual stress of the thick PZT film. Inaddition, in a film forming method of a PZT film by a sol-gel method,the process time becomes long due to stacking of 20 layers or more.

(2) A PZT Film by a Sputtering Method (for Example, See Patent Document1)

Patent Document 1 discloses a PZT film formed by a sputtering method.The PZT film has advantages such as a small leak current density,capability of epitaxial growth and high initial properties.

But, the PZT film has following drawbacks.

Since the PZT film is exposed to plasma during the film formation, it isdamaged easily by ions etc., the PZT film is imprinted, or thehysteresis is deformed and properties are likely to be deteriorated.Since an epitaxial growth proceeds slowly, the film forming time is aslong as several hours. Furthermore, since the manufacturing apparatusmakes use of a high vacuum and high temperature, the cost becomes highand the product unit price cannot be lowered. Moreover, since theformation of uniform plasma in the film forming is difficult, thevariation of film properties and film thickness of the PZT film becomeslarge to make mass productivity poor.

Especially when a sputtering method is employed for mass production,variation of the composition, thickness and various properties of PZTfilms are large due to the influence of erosion.

(3) A PZTN Film (for Example, See Patent Document 2)

Patent Document 2 discloses a ferroelectric film including aperovskite-structured ferroelectric substance represented by ABO₃, thedisclosure being a PZTN ferroelectric film in which theperovskite-structured ferroelectric substance is a PZT-basedferroelectric substance containing Pb²⁺ as A-site ions and containingZr⁴⁺ and Ti⁴⁺ as B-site ions, and containing Si²⁺ in the A-site asA-site compensation ions and containing Nb⁵⁺ in the B-site as B-sitecompensation ions.

But, the PZTN ferroelectric film has following drawbacks.

Since it contains Si²⁺ in the A-site as A-site compensation ions, theferroelectricity is deteriorated largely by the Si (see FIG. 5).Although it contains Si²⁺ in the A-site as A-site compensation ions andNb⁵⁺ in the B-site as B-site compensation ions, Si and Nb can notsufficiently prevent the deficiency of an oxygen ion, or notsufficiently suppress the leak current. Furthermore, when making a PZTNferroelectric film thick, a thick film is obtained, by a sol-gel method,through the use of a sol-gel solution having a large contact angle (forexample, 60° or more). Therefore, air bubbles enter easily into the PZTNferroelectric film.

RELATED TECHNICAL DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent No. 3377874

Patent Document 2: Japanese Patent No. 4171908

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As described above, the PZTN ferroelectric film contains Si²⁺ in theA-site as the A-site compensation ions and Nb⁵⁺ in the B-site as theB-site compensation ions, but Si and Nb cannot sufficiently prevent thedeficiency of oxygen ions.

That is, the conventional method performs control by replacing theA-site ions in a lead (2+) deficiency position with Si²⁺ and replacingthe B-site ions (4+) with Nb⁵⁺. However, according to repeated studiesby the present inventors, it has been found that Si can not sufficientlyattain a function of preventing oxygen ion deficiency to deteriorate theferroelectricity (see FIG. 5). It is like putting the cart before thehorse if Si lets ferroelectric substance properties deteriorate even ifan effect of preventing oxygen ion deficiency is exhibited. IF theprevention of the oxygen ion deficiency without Si is tried, two Nbatoms are necessary instead of one Si atom, and there is a problem ofincreasing the crystallization temperature as described in PatentDocument 2.

Furthermore, as described above, for the thickening of the conventionalPZTN ferroelectric film, the thickness is made large through the use ofa sol-gel solution having a large contact angle (for example, 60° ormore) by a sol-gel method, and thus there is a problem in which airbubbles enter easily into the PZTN ferroelectric film.

An aspect of the present invention aims at providing a PBNZTferroelectric film capable of preventing sufficiently the deficiency ofan oxygen ion, a sol-gel solution, a film forming method using thesol-gel solution, a ferroelectric material film formed by the filmforming method, and a method for producing a ferroelectric film.

Another aspect of the present invention aims at providing a sol-gelsolution into which air bubbles hardly enter when it is formed into athick film, a film forming method using the sol-gel solution, aferroelectric material film formed by using the film forming method, anda method for producing a ferroelectric film.

Means for Solving the Problems

In a ferroelectric film according to an aspect of the present invention,Bi³⁺ is added to a lead (2+) deficient position and, simultaneously,B-site ions (4+) are replaced with Nb⁵⁺ ions, which makes it possible toprevent at once one oxygen ion deficiency (2−) by equivalent Bi+Nb=2+,differing from conventional technologies.

(1) to (38) below are to explain a plurality of aspect of the presentinvention.

(1) A PBNZT ferroelectric film that is a ferroelectric film including aperovskite-structured ferroelectric substance represented by ABO₃, and

the perovskite-structured ferroelectric substance is a PZT-basedferroelectric substance containing Pb²⁺ as A-site ions and containingZr⁴⁺ and Ti⁴⁺ as B-site ions;

the A-site contains Bi³⁺ as A-site compensation ions; and

the B-site contains Nb⁵⁺ as B-site compensation ions.

(2) A PBNZT ferroelectric film that is a ferroelectric film including aperovskite-structured ferroelectric substance represented by ABO₃including an oxygen ion deficiency, and

the perovskite-structured ferroelectric substance is a PZT-basedferroelectric substance containing Pb²⁺ as A-site ions and containingZr⁴⁺ and Ti⁴⁺ as B-site ions;

the A-site contains Bi³⁺ as A-site compensation ions;

the B-site contains Nb⁵⁺ as B-site compensation ions; and

the total of a surplus valence number in the whole A-site by said A-sitecompensation ions and a surplus valence number in the whole B-site bysaid B-site compensation ions is the same as a deficient valence numbercorresponding to the amount of the oxygen ion deficiency or is smallerthan the deficient valence number.

(3) A PBNZT ferroelectric film that is a ferroelectric film including aperovskite-structured ferroelectric substance represented by(Pb_(1-X)Bi_(X))((TiZr)_(1-Y)Nb_(Y))O₃, wherein:

X is 1 to 10 mol %; and

Y is 1 to 10 mol %.

Meanwhile, preferably, an A-site contains Bi³⁺ as A-site compensationions and a B-site contains Nb⁵⁺ as B-site compensation ions.

(4) A PBNZT ferroelectric film that is a ferroelectric film including aperovskite-structured ferroelectric substance represented by(Pb_(1-X)Bi_(X))((TiZr)_(1-Y)Nb_(Y))O₃, and

X is 1 to 10 mol %; and

Y is 1 to 10 mol % and X=Y.

Meanwhile, preferably, an A-site contains Bi³⁺ as A-site compensationions and a B-site contains Nb⁵⁺ as B-site compensation ions.

(5) The PBNZT ferroelectric film according to the above (2), and theamount of oxygen ion deficiency is 20 mol % or less relative to thestoichiometric composition of the perovskite-structured ferroelectricsubstance.

(6) The PBNZT ferroelectric film according to any one of the above (1),(2) and (5), and

the content of the A-site compensation ions is 10 mol % or less relativeto the stoichiometric composition of the perovskite-structuredferroelectric substance; and

the content of the B-site compensation ions is 10 mol % or less relativeto the stoichiometric composition of the perovskite-structuredferroelectric substance.

(7) The PBNZT ferroelectric film, in which the ferroelectric filmaccording to any one of the above (1) to (6) has a pillar shape crystalstructure.

(8) The PBNZT ferroelectric film, in which the ferroelectric filmaccording to any one of the above (1) to (7) has scarcely air bubbles.

(9) The PBNZT ferroelectric film, in which the ferroelectric filmaccording to any one of the above (1) to (8) has a micro Vickershardness 600 to 1200 Hv (preferably 800 to 1000 Hv).

(10) A sol-gel solution for forming a ferroelectric film on a substrate,in which the sol-gel solution has a contact angle of 1 to not more than40° with respect to the substrate.

(11) The sol-gel solution according to the above (10), in which thecontact angle with respect to the substrate is 1 to not more than 20°.

(12) The sol-gel solution according to the above (10) or (11), in whichthe sol-gel solution includes a raw material solution includinghydrolysis polycondensation of an alkoxide raw material including Pb,Bi, Nb, Zr and Ti.

(13) The sol-gel solution according to the above (12), in which thesol-gel solution includes a polycarboxylic acid or a polycarboxylic acidester in the solvent.

(14) The sol-gel solution according to the above (13), in which thepolycarboxylic acid ester includes heteropolyacid ions.

(15) The sol-gel solution according to the above (14), in which theheteropolyacid ion has a Keggin type structure represented by followingFormula: [XM_(y)M′_(12-y)O₄₀]^(n−) (where X is a hetero atom, M is apolyatom, M′ is a polyatom different from M, n is a valence number, andy=1 to 11).

(16) The sol-gel solution according to the above (14), in which theheteropolyacid ion has a Keggin type structure represented by Formula:[XM₁₁O₃₉]^(n−) (where X is a hetero atom, M is a polyatom, and n is avalence number).

(17) The sol-gel solution according to the above (14), in which theheteropolyacid ion has a Keggin type structure represented by followingFormula: [XM_(z)M′_(11-z)O₃₉]^(n−) (where X is a hetero atom, M is apolyatom, M′ is a polyatom different from M, n is a valence number, andz=1 to 10).

(18) The sol-gel solution according to any one of the above (14) to(17), in which the sol-gel solution includes, among the heteropolyacidions, heteropolyacid ions according to any one of claims 7 to 10 in thatthe hetero atom includes the group consisting of B, Si, P, S, Ge, As,Mn, Fe and Co and the polyatom includes the group consisting of Mo, V,W, Ti, Al, Nb and Ta, as a part of a precursor structure of aferroelectric ceramics.

(19) The sol-gel solution according to any one of the above (12) to(18), in which the sol-gel solution includes at least one of a highviscosity polyhydric alcohol, glycol ethers, a lower alcohol and a basicalcohol in the solvent.

(20) The sol-gel solution according to any one of the above (12) to(19), in which:

the ferroelectric film includes a perovskite-structured ferroelectricsubstance represented by (Pb_(1-X)Bi_(X))((TiZr)_(1-Y)Nb_(Y))O₃;

X is 1 to 10 mol %;

Y is 1 to 10 mol %; and

the surplus lead addition amount included in the raw material solutionis 15 mol % or more.

(21) The sol-gel solution according to any one of the above (10) to(20), wherein the sol-gel solution includes polar solvents.

(22) The sol-gel solution according to the above (21), in which thepolar solvent or the like is any one of methyl ethyl ketone,1,4-dioxane, 1,2-dimethoxyethane acetamide, N-methyl-2-pyrrolidone,acetonitrile, dichloromethane, nitromethane, trichloromethane,dimethylformamide and monomethylformamide or a plurality of combinationsthereof.

(23) The sol-gel solution according to any one of the above (10) to(22), in which the sol-gel solution includes an unsaturated fatty acid.

(24) The sol-gel solution according to the above (23), in which:

the unsaturated fatty acid is any one of monounsaturated fatty acid,diunsaturated fatty acid, triunsaturated fatty acid, tetraunsaturatedfatty acid, pentaunsaturated fatty acid and hexaunsaturated fatty acidor a plurality of combinations thereof;

the monounsaturated fatty acid is any one of crotonic acid, myristoleicacid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid,gadoleic acid, eicosenoic acid, erucic acid and nervonic acid or aplurality of combinations thereof;

the diunsaturated fatty acid is any one of linoleic acid, eicosadienoicacid and docosadienoic acid or a plurality of combinations thereof;

the triunsaturated fatty acid is any one of linolenic acid, pinolenicacid, eleostearic acid, mead acid, dihomo-γ-linolenic acid andeicosatrienoic acid or a plurality of combinations thereof;

the tetraunsaturated fatty acid is any one of stearidonic acid,arachidonic acid, eicosatetraenoic acid and adrenic acid or a pluralityof combinations thereof;

the pentaunsaturated fatty acid is any one of bosseopentaenoic acid,eicosapentaenoic acid, osbond acid, clupanodonic acid andtetracosapentaenoic acid or a plurality of combinations thereof; and

the hexaunsaturated fatty acid is any one of docosahexaenoic acid andnisinic acid or a plurality of combinations thereof.

(25) A method for producing a ferroelectric film, in which the sol-gelsolution according to any one of the above (10) to (24) is used forproduction of the PBNZT ferroelectric film according to any one of theabove (1) to (9).

(26) A method for producing a ferroelectric film, in which the sol-gelsolution according to any one of the above (10) to (24) is used forproduction of a ferroelectric film having a relative permittivity of 400or more (more preferably relative permittivity of 600 or more).

(27) A ferroelectric film being formed by the method for producing aferroelectric film according to the above (26) and having a relativepermittivity of 400 or more (more preferably a relative permittivity of600 or more).

(28) A film forming method, including the steps of:

coating the sol-gel solution according to any one of the above (10) to(24) on a substrate to form a coated film on the substrate;

temporarily burning the coated film;

repeating the formation of the coated film and the temporary burning aplurality of times to form a ferroelectric material film including theplural number of coated films on the substrate.

(29) The film forming method according to the above (28), in which:

the ferroelectric material film has a thickness of more than 300 nm; and

the ferroelectric material film is subjected to a heat treatment tocrystallize collectively the ferroelectric material film.

(30) A method for producing a ferroelectric film, including the stepsof:

forming a ferroelectric material film on a substrate by using the filmforming method according to the above (28) or (29); and

heat-treating the ferroelectric material film to form a ferroelectricfilm including a perovskite-structured ferroelectric substance obtainedby crystallizing the ferroelectric material film, in which theferroelectric film is the PBNZT ferroelectric film according to any oneof claims 1 to 9.

(31) A method for producing a ferroelectric film including the steps of:

forming a ferroelectric material film on a substrate by using the filmforming method according to (28) or (29); and

heat-treating the ferroelectric material film to form, on the substrate,a ferroelectric film having a relative permittivity of 400 or more (morepreferably a relative permittivity of 600 or more) obtained bycrystallizing the ferroelectric material film.

(32) A ferroelectric film being formed by the method for producing theferroelectric film according to the above (31) and having a relativepermittivity of 400 or more (more preferably a relative permittivity of600 or more).

(33) A method for producing a ferroelectric film including the steps of:

preparing a sol-gel solution including a raw material solutionincluding: a hydrolysis polycondensation of an alkoxide raw materialincluding Pb, Bi, Nb, Zr and Ti and heteropolyacid; and polar solventsand unsaturated fatty acids;

coating the sol-gel solution on a substrate to form a coated film on thesubstrate;

subjecting the coated film to temporary burning at a temperature of 25to 450° C. to form a ferroelectric material film on the substrate; and

heat-treating the ferroelectric material film at a temperature of 450 to800° C. to produce a ferroelectric film including aperovskite-structured ferroelectric substance obtained by crystallizingthe ferroelectric material film.

(34) The method for producing a ferroelectric film according to theabove (29), wherein, when a ferroelectric material film is formed on thesubstrate, the formation of the coated film and the temporary burningare repeated a plurality of times to form a ferroelectric material filmincluding the plurality of coated films on the substrate.

(35) The method for producing a ferroelectric film according to theabove (33) or (34), wherein the ferroelectric film is the PBNZTferroelectric film according to any one of claims 1 to 9.

(36) The method for producing a ferroelectric film according to theabove (33) or (34), in which the ferroelectric film has a relativepermittivity of 400 or more (more preferably a relative permittivity of600 or more).

(37) A ferroelectric film being formed by the method for producing aferroelectric film according to the above (36) and having a relativepermittivity of 400 or more (more preferably a relative permittivity of600 or more).

(38) The method for producing a ferroelectric film according to any oneof the above (30), (31) and (33) to (36), in which the surface of thesubstrate has a (111)-oriented Pt or Ir film.

Advantage of the Invention

According to an aspect of the present invention, it is possible toprovide a PBNZT ferroelectric film capable of preventing sufficientlythe deficiency of an oxygen ion, a sol-gel solution, a film formingmethod using the sol-gel solution, a ferroelectric material film formedby the film forming method, or a method for producing a ferroelectricfilm.

Furthermore, according to another aspect of the present invention, it ispossible to provide a sol-gel solution into which air bubbles hardlyenter even if a film is made thick, a film forming method using thesol-gel solution, a ferroelectric material film formed by the filmforming method, or a method for producing a ferroelectric film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph showing the ferroelectric film that is a sample 1in Example.

FIG. 2 is a photograph showing a PZT film in Comparative Example forperforming comparison with the sample 1 shown in FIG. 1.

FIG. 3A is a drawing showing a SEM cross-sectional image of the PZT filmin Comparative Example shown in FIG. 2, and FIG. 3B is a drawing showinga SEM cross-sectional image of the ferroelectric film of the sample 1shown in FIG. 1.

FIGS. 4A to 4C are drawings showing the result of measuring a leakcurrent density for each of ferroelectric films of samples 1 to 3.

FIG. 5 is a drawing showing the result of performing hysteresisevaluation of the PBNZT ferroelectric film in the Example of the presentinvention and a conventional PZT to which Si is added.

FIG. 6 is a drawing showing the result of performing hysteresisevaluation of the PBNZT ferroelectric film in the Example of the presentinvention and a conventional PZT to which Si is added.

FIG. 7A is a photograph showing a sample of a 5 μm-PBNZT thick film4-inch wafer, and FIG. 7B is a photograph showing a sample of a 1.5μm-PBNZT thick film 6-inch wafer.

FIG. 8 shows a TEM cross-sectional image of a 2 μm-PBNZT thick film asthe drawing denoted by “newly developed,” and a TEM cross-sectionalimage of a PZT film (FIG. 3A) of Comparative Example for Example 1 asthe drawing denoted by “a conventional product.”

FIG. 9A is a drawing showing a SEM cross-sectional image of a 1 μm-PBNZTthick film, FIG. 9B is a drawing showing a SEM cross-sectional image ofa 1.5 μm-PBNZT thick film, FIG. 9C is a drawing showing a SEMcross-sectional image of a 2 μm-PBNZT thick film, FIG. 9D is a drawingshowing a SEM cross-sectional image of a 3 μm-PBNZT thick film, FIG. 9Eis a drawing showing a SEM cross-sectional image of a 4 μm-PBNZT thickfilm, and FIG. 9F is a drawing showing a SEM cross-sectional image of a5 μm-PBNZT thick film.

FIG. 10A is a drawing showing a result of performing the hysteresisevaluation of a 3 μm-PBNZT thick film, FIG. 10B is a drawing showing aresult of performing the hysteresis evaluation of a 4 μm-PBNZT thickfilm, and FIG. 10C is a drawing showing a result of the hysteresisevaluation of a 5 μm-PBNZT thick film.

FIGS. 11A to 11C are drawings showing results of evaluating thecrystallinity of the PBNZT thick film in the Example by XRD diffraction,FIG. 11D is a drawing showing a result of performing the hysteresisevaluation of the PBNZT thick film in FIG. 11A, FIG. 11E is a drawingshowing a result of performing the hysteresis evaluation of the PBNZTthick film in FIG. 11B, and FIG. 11F is a drawing showing a result ofperforming the hysteresis evaluation of the PBNZT thick film in FIG.11C.

FIG. 12 is a schematic view showing crystals of PBNZT thick filmsoriented in (001), (111) and (110), respectively.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be explained indetail by using the drawings. But, a person skilled in the art canunderstand easily that the present invention is not limited to theexplanation below, but that forms and details thereof can be changedvariously without deviating from the purport and the scope of thepresent invention. Accordingly, the present invention should not beconstrued with the limitation to the content of the description ofembodiments shown below.

The PBNZT ferroelectric film according to the embodiment includes aperovskite-structured ferroelectric substance represented by ABO₃. Theperovskite-structured ferroelectric substance is a PZT-basedferroelectric substance containing Pb²⁺ as A-site ions and containingZr⁴⁺ and Ti⁴⁺ as B-site ions, and containing Bi³⁺ at the A-site asA-site compensation ions, and containing Nb⁵⁺ at the B-site as B-sitecompensation ions.

In detail, the ferroelectric film includes a perovskite-structuredferroelectric substance represented by ABO₃ including an oxygen iondeficiency, the perovskite-structured ferroelectric substance is aPZT-based ferroelectric substance containing Pb²⁺ as A-site ions andcontaining Zr⁴⁺ and Ti⁴⁺ as B-site ions, the A-site contains Bi³⁺ asA-site compensation ions and the B-site contains Nb⁵⁺ as B-sitecompensation ions, and the total of a surplus valence number in thewhole A-site due to the A-site compensation ions and a surplus valencenumber in the whole B-site due to the B-site compensation ions is equalto a deficient valence number corresponding to the amount of the oxygenion deficiency, or smaller than the deficient valence number.

The amount of the oxygen ion deficiency is preferably 20 mol % or lessrelative to the stoichiometric composition of the perovskite-structuredferroelectric substance. Furthermore, the content of the A-sitecompensation ions is preferably 10 mol % or less relative to thestoichiometric composition of the perovskite-structured ferroelectricsubstance. Moreover, the content of the B-site compensation ions ispreferably 10 mol % or less relative to the stoichiometric compositionof the perovskite-structured ferroelectric substance.

Specifically, the ferroelectric film includes a perovskite-structuredferroelectric substance represented by(Pb_(1-X)Bi_(X))((TiZr)_(1-Y)Nb_(Y))O₃.

X is preferably 1 to 10 mol %, and Y is preferably 1 to 10 mol %.

According to the embodiment, since Bi has a stable valence number +3, ithas a valence number greater than the A-site ion by +1, and since Nb hasa stable valence number +5, it has a valence number greater than theB-site ion by +1. Therefore, the surplus valence number becomes +2,thereby being able to prevent reliably the deficiency of an oxygen (−2valence) ion. That is, by replacing the A-site ion with the added Bi ionand replacing the B-site ion with the added Nb ion, it is possible toprevent the deficiency of an oxygen ion, to bring the state close tocomplete oxidation, and to bring the charge neutrality in the perovskitestructure in to existence. For example, when a perovskite-structuredferroelectric substance represented by ABO₃ is a PZT-based ferroelectricsubstance, a ferroelectric film is formed so that the total of thesurplus valence number +1 valence ((Bi: +3 valence)−(Pb: +2 valence)=(+1valence)) caused by the addition of the A-site compensation ions and thesurplus valence number +1 valence caused by the addition of the B-sitecompensation ions ((Nb: +5 valence)−(Ti: +4 valence)=(+1 valence)), thatis, Bi addition amount×(+1 valence)+Nb addition amount×(+1 valence)becomes not more than the deficient valence number corresponding to theoxygen ion deficiency amount (oxygen ion deficiency amount×(−2valence)).

Next, the method for producing a ferroelectric film according to theembodiment will be explained in detail. The ferroelectric film includesa perovskite-structured ferroelectric substance represented by(Pb_(1-X)Bi_(X))((TiZr)_(1-Y)Nb_(Y))O₃, where X is 1 to 10 mol % and Yis 1 to 10 mol %.

[1] Substrate

On a substrate such as a 6-inch Si wafer, a foundation film oriented ina prescribed crystal plane is formed. As the foundation film, forexample, a (111)-oriented Pt film or Ir film is used.

[2] Sol-Gel Solution

A sol-gel solution having a contact angle of 40° or less, preferably 20°or less with the substrate is prepared.

The sol-gel solution is fabricated as follows.

(1) Fabrication of a Ceramic Precursor (PZT Condensation Polymer)

In detail, anhydrous lead acetate Pb(CH₃COO)₂, zirconium isopropoxideZr(O-i-C₃H₇)₄, and titanium isopropoxide Ti(O-i-C₃H₇)₄ are employed asstarting materials, and a gel obtained by a reaction of lead acetate andmetal alkoxide by distillation and reflux in 2-methoxyethanol and analcohol exchange reaction is set to be a precursor raw material forforming PZT ceramics.

(2-1) Element Addition 1

To the precursor raw material for forming PZT ceramics, the octylatethat is any one of Nb octylate and Bi octylate, or the octylates thatare both Nb octylate and Bi octylate are added. Preferably, when any oneis to be added, it is added in 10 mol % or less, and, when both are tobe added, each is added in 5 mol % or less. Furthermore, preferably, oneor more of octylates of Mo, V, W, Al, Ta, B, Si, P, S, Ge, As, Fe, Mn,Co are added in 3 mol % or less, respectively.

(2-2) Element Addition 2

A divalent carboxylic acid or a divalent carboxylic acid ester is addedto the solvent in an amount not less than the equivalent volume relativeto the added element. As the divalent carboxylic acid, the use ofsuccinic acid, oxalic acid, malonic acid, adipic acid, maleic acid,fumaric acid or the like is preferable, and, as the divalent carboxylicacid ester, the use of at least one kind selected from succinic acidesters, malonic acid esters and maleic acid esters is preferable.Specific examples of these esters include dimethyl succinate, dimethylmaleate, and dimethyl malonate. These divalent carboxylic acid estersdissociate in the presence of alcohol to show the action as divalentcarboxylic acid.

The divalent carboxylic acid ester preferably contains a heteropolyacidion containing, for example, Mn²⁺ as a hetero ion.

The sol-gel solution contains, as a part of the precursor structure ofthe ferroelectric substance ceramics, a heteropolyacid ion having aKeggin type structure with a non-centrosymmetric molecular structure toexpress nonlinearity as a constituent component wherein at least one ofthe polyatom of the heteropolyacid ion is deficient or a part of thepolyatom of the heteropolyacid ion is replaced with another atom.

The heteropolyacid ion is one having a Keggin type structure representedby following Formula [XM_(y)M′_(12-y)O₄₀]^(n−) (where X is a heteroatom, M is a polyatom, M′ is a polyatom different from M, n is a valencenumber, and y=1 to 11), and the heteropolyacid ion is contained as apart of the precursor structure of the ferroelectric substance ceramics.

Furthermore, the heteropolyacid ion may be one having a Keggin typestructure represented by Formula: [XM₁₁O₃₉]^(n−) (where X is a heteroatom, M is a polyatom, and n is a valence number), and theheteropolyacid ion is contained as a part of the precursor structure ofthe ferroelectric substance ceramics.

Moreover, the heteropolyacid ion is one having a Keggin type structurerepresented by following Formula: [XM_(z)M′_(11-z)O₃₉]^(n−) (where X isa hetero atom, M is a polyatom, M′ is a polyatom different from M, n isa valence number, and z=1 to 10), and the heteropolyacid ion iscontained as a part of the precursor structure of the ferroelectricsubstance ceramics.

It is also possible that, in the heteropolyacid ion, the hetero atomincludes the group consisting of B, Si, P, S, Ge, As, Mn, Fe and Co andthe polyatom includes the group consisting of Mo, V, W, Ti, Al, Nb andTa, and the heteropolyacid ion may be contained as a part of theprecursor structure of the ferroelectric substance ceramics.

The sol-gel solution preferably contains polar solvents. The polarsolvent or the like is any one of methyl ethyl ketone, 1,4-dioxane,1,2-dimethoxyethane acetamide, N-methyl-2-pyrrolidone, acetonitrile,dichloromethane, nitromethane, trichloromethane, dimethylformamide andmonomethylformamide, or a plurality of combinations thereof.

(3) Film Thickening (High Viscosity Polyhydric Alcohol)

To a precursor raw material for forming PZT ceramics, a high viscositypolyhydric alcohol is added. Consequently, it becomes possible to makethe film thick when the sol-gel solution is coated. Meanwhile, as thehigh viscosity polyhydric alcohol, preferably either of ethylene glycolor diethylene glycol, or both of these are added in a volume of ½ orless of the whole.

(4) Deaeration (Unsaturated Fatty Acid)

The sol-gel solution contains preferably unsaturated fatty acid in notmore than ⅓ of the whole volume. Consequently, the inside of the coatedfilm obtained by coating the sol-gel solution can be deaired.

The unsaturated fatty acid is any one of monounsaturated fatty acid,diunsaturated fatty acid, triunsaturated fatty acid, tetraunsaturatedfatty acid, pentaunsaturated fatty acid and hexaunsaturated fatty acid,or a plurality of combinations thereof.

Examples of the monounsaturated fatty acids include crotonic acid,myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenicacid, gadoleic acid, eicosenoic acid, erucic acid and nervonic acid, andany, or a plurality of combinations thereof may be used.

Examples of the diunsaturated fatty acids include linoleic acid,eicosadienoic acid and docosadienoic acid, and any, or a plurality ofcombinations thereof may be used.

Examples of the triunsaturated fatty acids include linolenic acid,pinolenic acid, eleostearic acid, mead acid, dihomo-γ-linolenic acid andeicosatrienoic acid, and any, or a plurality of combinations thereof maybe used.

Examples of the tetraunsaturated fatty acids include stearidonic acid,arachidonic acid, eicosatetraenoic acid and adrenic acid, and any, or aplurality of combinations thereof may be used.

Examples of the pentaunsaturated fatty acids include bosseopentaenoicacid, eicosapentaenoic acid, osbond acid, clupanodonic acid andtetracosapentaenoic acid, and any, or a plurality of combinationsthereof may be used.

Examples of the hexaunsaturated fatty acids include docosahexaenoic acidand nisinic acid, and either, or a plurality of combinations thereof maybe used.

(5) A Solvent for a Hardly Soluble Component (Glycol Ether)

To the sol-gel solution, glycol ether is preferably added as a solventfor a hardly soluble component. Consequently, it becomes possible todissolve a hardly soluble component in the sol-gel solution. The glycolether includes ethylene glycol-based ethers and propylene glycol-basedethers based on respective groups of aliphatic series such as methyl,n-propyl, i-propyl, n-butyl, i-butyl, hexyl and 2-ethylhexyl, allyl andphenyl having a double bond, and benzyl. They are liquids having nocolor and a little smell, and provided with properties of both alcoholsand ethers because they have an ether group and a hydroxyl group in themolecule. That is, the liquid functions as a solvent for a hardlysoluble component, and, in addition, functions as alcohol, which is afunction of improving the wettability with the substrate. Among these,dialkyl glycol ether is obtained by replacing a hydrogen at the end ofethylene glycol, diethylene glycol or triethylene glycol with an alkylgroup, and has two or more ether groups in the molecule and is used as asolvent for taking the solubility very seriously. An ester with aceticacid is employed for the purpose of improving the solubility, and esterswith acrylic acid or methacrylic acid are employed for the purpose as aviscosity modifier.

It is preferable to use any one, or a plurality of combinations of theabove-mentioned glycol ethers. Furthermore, glycol ether is preferablyadded until the dissolution of the unsaturated fatty acid.

(6) Stable Coating on a Pt/Si Substrate (Lower Alcohol)

Lower alcohol is preferably added to the sol-gel solution. Consequently,it becomes possible to stably coat the sol-gel solution on the Pt/Sisubstrate. As the lower alcohol, particularly, alcohols having fourcarbons or less are preferable, and any one of, or a plurality ofcombinations of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol,2-methyl-1-propanol, 2-butanol and 2-methyl-2-propanol is preferable.The alcohol has a good compatibility with a Pt electrode. It ispreferable to adjust the addition amount of the lower alcohol so that,when the sol-gel solution is coated on the substrate, the contact angleof the coated film with the substrate is 1 to 40° (preferably 1 to 20°).If the addition amount of the lower alcohol is increased too much, thethickness of the coated film per one layer becomes too thin, and,therefore, the addition amount is desirably three times or less thewhole volume.

(7) Stabilization of the Solution (Basic Alcohol)

To the sol-gel solution, basic alcohol for stabilizing the solution ispreferably added. Consequently, it becomes possible to stabilize thesol-gel solution.

In detail, it is preferable to add one or more of 2-aminoethanol,2-(2-aminoacylamino) ethanol, 2-(2-aminoethoxy) ethanol,5-amino-2,3-dihydrophthalazine-1,4-dione, 2-amino-3-phenyl-1-propanol,2-amino-1-butanol and 4-amino-1-butanol among aminoalcohols that arebasic alcohols to the sol-gel solution to adjust so that pH is 5 to 7.

[3] Coating of the Sol-Gel Solution on a Substrate

On a substrate having a (111)-oriented Pt film formed on the surface of6-inch Si wafer, the sol-gel solution was coated, and the contact angleof the sol-gel solution with the substrate was measured to give theresult of 20° or less. Meanwhile, the contact angle with the substratecan be 1 to 40° (preferably 1 to 20°).

The sol-gel solution is coated onto a substrate by a spin-coating methodto form a coated film on the substrate, the coated film is subjected totemporary burning at a temperature of 25 to 450° C. (preferably atemperature of 450° C.), and, by repeating the formation of the coatedfilm and the temporary burning a plurality of times, a ferroelectricmaterial film including a plurality of coated films is formed on thesubstrate. Meanwhile, in the embodiment, the sol-gel solution is coatedby a spin-coating method, but, it is not limited to the spin-coatingmethod and the coating by other coating methods is also possible,including, for example, a doctor blade method, a screen printing method,a dip-coating method, a spray-coating method, an evaporation method, anatmospheric pressure plasma CVD method or the like.

[4] A Crystallization Method

A heat treatment of a ferroelectric material film at a temperature of450 to 800° C. (preferably a temperature of 700° C.) makes it possibleto crystallize the ferroelectric material film. The condition of theheat treatment at this time is to perform burning in a pressurizedoxygen atmosphere of 2 to 9.9 atm, at a temperature increase rate of 100to 150° C./sec for 1 to 5 minutes. In addition, the thickness of aferroelectric material film when crystallizing collectively theferroelectric material film is preferably a thickness exceeding 300 nm.

The ferroelectric film thus fabricated contains scarcely air bubbleseven when it is a thick film having a thickness of 500 or more. In otherwords, by forming the film in this manner, a good and thick film can beformed. The reason is because the film has a structure in which organiccomponents have disappeared almost in the thickness direction, and thefilm scarcely shrinks in the substrate plane, the shrinkage being at thelevel of being cancelled by the expansion due to oxidation. Accordingly,the substrate has scarcely warpage.

It should be noted that the repetition of the formation andcrystallization of the ferroelectric material film also makes itpossible to form a ferroelectric film having a thickness of 2 μm ormore.

Moreover, in the embodiment, the method for producing the ferroelectricfilm, which includes the perovskite-structured ferroelectric substancerepresented by (Pb_(1-X)Bi_(X))((TiZr)_(1-Y)Nb_(Y))O₃ where X is 1 to 10mol % and Y is 1 to 10 mol %, is explained. And, the use of the sol-gelsolution or the film forming method according to the embodiment makes itpossible to produce ferroelectric films other than the above-mentionedferroelectric film having a relative permittivity of 400 or more (morepreferably a relative permittivity of 600 or more).

EXAMPLES Example 1

On a 6-inch Si wafer, via a silicon oxide film, a Ti film of 10 to 30 nmis formed by a sputtering method. In detail, the film was formed by anRF sputtering method. The Ti film functions as adhesion layer ofplatinum and silicon oxide. The Ti film was formed under thefilm-forming conditions of argon gas pressure 0.2 Pa and power sourceoutput 0.12 kW for 20 minutes. The film formation was performed at thesubstrate temperature of 200° C.

Next, the Ti film is subjected to a heat treatment by RTA (Rapid ThermalAnneal) at the temperature of 650° C. for 5 minutes. The heat treatmentwas performed in an oxygen atmosphere at 9.9 atm and 100° C./s.

Then, on the Ti film, a 100 nm first Pt film is formed by a sputteringmethod at the temperature of 550 to 650° C. The film was formed at argongas pressure 0.4 Pa, source output DC 100 W and film-forming time 25minutes.

After that, on the first Pt film, a 100 nm second Pt film is formed byan evaporation method at ordinary temperatures. The film was formed at3.3×10⁻³ Torr, source output 10 kV and film-forming time 4 minutes.

Next, the Si wafer is subjected to a heat treatment by RTA at thetemperature of 650 to 750° C. for 1 to 5 minutes. In this way, a 6-inchSi wafer having a (111)-oriented Pt film formed on the surface isprepared.

Then, a sol-gel solution having a contact angle of 40° or less,preferably 20° or less with the 6-inch Si wafer is prepared. In detail,the sol-gel solution contains a raw material solution containing aheteropolyacid containing Pb, Bi, Nb, Zr and Ti, polar solvents, andunsaturated fatty acids.

The raw material solution for forming a PBNZT ferroelectric film iscomposed of a mixture with a heteropolyacid being a polyacid of a(X_(l)M_(m)O_(n))^(x−) type in which a hetero atom is inserted into ametal oxygen acid skeleton. The polyatom includes M=Mo, V, W, Ti, Al, Nband Ta, the hetero atom means elements other than H and C, and a sol-gelsolution for forming an oxide film preferably including M=B, Si, P, S,Ge, As, Fe, Co and Bi.

The polar solvent or the like is any one of methyl ethyl ketone,1,4-dioxane, 1,2-dimethoxyethane acetamide, N-methyl-2-pyrrolidone,acetonitrile, dichloromethane, nitromethane, trichloromethane,dimethylformamide and monomethylformamide, or a plurality ofcombinations thereof.

As to the unsaturated fatty acids, examples of the monounsaturated fattyacids include crotonic acid, myristoleic acid, palmitoleic acid, oleicacid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid,erucic acid and nervonic acid, examples of the diunsaturated fatty acidsinclude linoleic acid, eicosadienoic acid and docosadienoic acid,examples of the triunsaturated fatty acids include linolenic acid,pinolenic acid, eleostearic acid, mead acid, dihomo-γ-linolenic acid andeicosatrienoic acid, examples of the tetraunsaturated fatty acidsinclude stearidonic acid, arachidonic acid, eicosatetraenoic acid andadrenic acid, examples of the pentaunsaturated fatty acids includebosseopentaenoic acid, eicosapentaenoic acid, osbond acid, clupanodonicacid and tetracosapentaenoic acid, and examples of the hexaunsaturatedfatty acids include docosahexaenoic acid and nisinic acid.

Next, by coating, by a spin-coating method, the sol-gel solution on the6-inch Si wafer covered with the Pt electrode, a first layer coated filmis formed on the Si wafer. In detail, the sol-gel solution 500 μL wascoated, the rotation speed of the coated wafer is increased from 0 to500 rpm in 3 seconds, the rotation speed of 500 rpm was held for 3seconds, then the coated wafer was rotated at 2500 rpm for 60 seconds,and the rotation was stopped.

Next, the first layer coated film is heated at a temperature of 175° C.for 1 minute by a hot plate, and after that, is subjected to temporaryburning at the temperature of 450° C. for 5 minutes. Consequently, onthe Si wafer, a first layer ferroelectric substance material amorphousfilm having thickness 100 nm is formed.

Subsequently, in the same way as that in the first layer coated film, asecond layer coated film is formed on the first ferroelectric materialfilm. Subsequently, in the same way as that in the first layer coatedfilm, the second layer coated film is heated to be subjected totemporary burning. Consequently, on the first layer ferroelectricmaterial film, the second layer ferroelectric material film havingthickness of 100 nm is formed.

Then, in the same way as that in the second layer coated film, a thirdlayer coated film is formed on the second layer ferroelectric materialfilm. Next, in the same way as that in the first layer coated film, thethird layer coated film is heated to be subjected to temporary burning.Consequently, on the second layer ferroelectric material film, the thirdlayer ferroelectric material film having a thickness of 100 nm isformed.

Subsequently, in the same way as that in the first layer coated film, afourth layer coated film is formed on the third layer ferroelectricmaterial film. Next, in the same way as that in the first layer coatedfilm, the fourth layer coated film is heated to be subjected totemporary burning. Consequently, on the third layer ferroelectricmaterial film, the fourth layer ferroelectric material film having athickness of 100 nm is formed.

Subsequently, in the same way as that in the first layer coated film, afifth layer coated film is formed on the fourth layer ferroelectricmaterial film. Next, in the same way as that in the first layer coatedfilm, the fifth layer coated film is heated to be subjected to temporaryburning. Consequently, on the fourth layer ferroelectric material film,the fifth layer ferroelectric material film having a thickness of 100 nmis formed. In this way, the ferroelectric material film having athickness of 500 nm, including five layers can be formed.

Next, a heat treatment of the ferroelectric material film by pressurizedRTA crystallizes the ferroelectric material film to form theferroelectric film. At this time, the heat treatment condition was atemperature increase rate 120° C./sec in a pressurized oxygen atmospherehaving an oxygen partial pressure of 9.9 atm, which instantaneouslyincreased the temperature up to 700° C. and held the temperature of 700°C. for 1 minute, thereby crystallizing the ferroelectric material film.

Next, on the ferroelectric material film, in the same way as above, bythe repetition of formation, heating and temporary burning of the coatedfilm, a ferroelectric material film having a thickness of 500 nm,including five layers is further formed. By crystallizing theferroelectric material film in the same way as above, a ferroelectricfilm is formed, and the formation and crystallization of theferroelectric material film is further repeated twice in the same way asabove. Consequently, a sample 1, in which a ferroelectric film includinga thick film having 2 μm is formed on the Si wafer, can be obtained.

Next, samples 2 and 3 having a ferroelectric film formed on a Si waferare fabricated. Each of the samples 2 and 3 is fabricated in the sameway as in sample 1, except that heat treatment conditions whencrystallizing the ferroelectric material film are different from thosein sample 1.

The heat treatment condition of the sample 2 was a temperature increaserate 120° C./sec in a pressurized oxygen atmosphere having an oxygenpartial pressure of 5 atm, which instantaneously increased thetemperature of the sample 2 up to 700° C. and held the temperature of700° C. for 1 minute, thereby crystallizing the sample 2.

The heat treatment condition of the sample 3 was a temperature increaserate 120° C./sec in a pressurized oxygen atmosphere having an oxygenpartial pressure of 7.5 atm, which instantaneously increased thetemperature of the sample 3 up to 700° C. and held the temperature of700° C. for 1 minute, thereby crystallizing the sample 3.

FIG. 1 is a photograph showing the ferroelectric film of the sample 1.

FIG. 2 is a photograph showing a conventional PZT film having thicknessof 1 μm formed on a 3-inch Si wafer for performing comparison with thesample 1 shown in FIG. 1.

While the ferroelectric film of the sample 1 shown in FIG. 1 has nointerference color, the PZT film in Comparative Example shown in FIG. 2has interference color.

FIG. 3A is a drawing showing the SEM cross-sectional image of the PZTfilm in Comparative Example shown in FIG. 2, and FIG. 3B is a drawingshowing the SEM cross-sectional image of the ferroelectric film of thesample 1 shown in FIG. 1.

It can be seen that the PZT film in Comparative Example shown in FIG. 3Ahas bubbles produced and has poor film quality. In contrast, it can beseen that the ferroelectric film of the sample 1 shown in FIG. 3B has apillar shape crystal structure or a columnar crystal structure, and, inspite of a thick film having thickness 2 μm, contains almost no bubbleto give a very good film quality.

FIG. 4A is a drawing showing the result of measuring a leak currentdensity for the ferroelectric film of the sample 1, FIG. 4B is a drawingshowing the result of measuring a leak current density for theferroelectric film of the sample 2, and FIG. 4C is a drawing showing theresult of measuring a leak current density for the ferroelectric film ofthe sample 3.

As shown in FIGS. 4A to 4C, it was confirmed that each of leak currentdensities of samples 1 to 3 is 10⁻⁹ A/cm², 10⁻¹⁰ A/cm², and 10⁻¹⁰ A/cm²,and that each of samples 1 to 3 has an extremely small leak currentdensity.

Next, micro Vickers hardness was measured for each of ferroelectricfilms of samples 1 to 3, and each was 800 to 1000 Hv.

Next, relative permittivity was measured for each of ferroelectric filmsof samples 1 to 3, and each was 600 or more.

FIGS. 5 and 6 are drawings showing the result of performing hysteresisevaluation of the PBNZT ferroelectric film in the Example of the presentinvention and a conventional PZT to which Si is added.

The hysteresis of the present invention shown in FIG. 5 is thehysteresis of the PBNZT ferroelectric film to which Bi 5 mol % and Nb 5mol % are added. This PBNZT ferroelectric film corresponds to the sampleshown in FIG. 3B. The hysteresis of the Si-added PZT of the conventionalexample shown in FIG. 5 is the hysteresis of PZT to which Si 5 mol % andNb 5 mol % are added.

The hysteresis of the present invention shown in FIG. 6 is thehysteresis of the PBNZT ferroelectric film to which Bi 10 mol % and Nb10 mol % are added. The PBNZT ferroelectric film is fabricated by thefabrication method in the Example. The hysteresis of the Si-added PZT ofthe conventional example shown in FIG. 6 is the hysteresis of the PZT towhich Si 5 mol % and Nb 20 mol % are added.

It was confirmed that, as shown in FIGS. 5 and 6, the ferroelectric filmof the present invention has an excellent hysteresis property ascompared with the conventional Si-added PZT. Meanwhile, the reason whythe hysteresis property of the conventional PZT is worse than that ofthe present invention is considered that Si can not sufficiently performthe function of preventing oxygen ion deficiency, and that the additionof Si deteriorates the ferroelectricity. Hereinafter, detailedexplanation will be given.

When the PBNZT (Bi: 5 mol %, Nb: 5 mol %) of the present invention wascompared with the conventional example to which Si and Nb are added (Si:5 mol %, Nb: 5 mol %), in the case of the conventional example, thehysteresis deteriorated largely when Si was added in 2 mol % or more, asshown in FIG. 5. That is, it is considered that Si works as a lowpermittivity layer to deteriorate the hysteresis property because somepercentage of the applied voltage is applied to a low permittivitylayer.

Next, according to the present invention, Bi 10 mol % and Nb 10 mol %were added, and, for comparison, since the addition of Nb 20 mol % waseffective in the conventional example, Nb 20 mol % and Si 5 mol % wereadded simultaneously. As the result, as shown in FIG. 6, cleardifference appeared. Since the different Nb addition amount resulted ina different anti-electric field, there appeared a large difference inresidual polarization value that was also considered as the influence ofSi.

Example 2

A raw material solution for forming a PBNZT ferroelectric film having apH of 6.8, a viscosity of 80 cps and a contact angle of 25° relative toPt was fabricated by adding raw material liquids as a formula below.[{(25 mol % PZT sol-gel solution (solvent: ethanol, surplus lead 25%)+5mol % niobium octylate+5 mol % bismuth octylate+3 mol % manganeseoctylate+15 mol % dimethyl succinate)+½ volume 2n butoxy ethanol}+⅛volume (oleic acid 60%+linoleic acid 30%+α-linolenic acid 9%+stearicacid 0.4%+stearoleic acid 0.3%+erucic acid 0.3%)+⅛ volume ethylmethylether]+⅕ volume dimethylaminoethanol   (formula)

Meanwhile, “volume” in the above formula means an amount stored in somevessel represented by a volume, which has a unit of cubic meter (m³),litter (l), or the like.

Next, in the same way as in Example 1, a 4-inch or 6-inch Si waferhaving a (111)-oriented Pt film formed on the surface is prepared, andthe above-mentioned raw material solution for forming PBNZTferroelectric film is coated on the Si wafer covered with the Ptelectrode by a spin-coating method. Consequently, on the Si wafer, afirst layer coated film is formed. In detail, the solution 1.5 cc forthe 4-inch wafer (3 cc for the 6-inch wafer) was coated, the rotationspeed of the coated wafer is increased from 0 to 500 rpm in 3 seconds,the rotation speed of 500 rpm was held for 5 seconds, then the coatedwafer was rotated at 1500 rpm for 90 seconds and at 3000 rpm for 30seconds, and the rotation was stopped.

Next, the first layer coated film was heated and dried at a temperatureof 250° C. for 30 seconds by a hot plate, and, after that, was subjectedto temporary burning at a temperature of 450° C. for 30 seconds.Consequently, on the Si wafer, a first layer ferroelectric substancematerial amorphous film having thickness 250 nm was formed.

Subsequently, in the same way as in the first layer coated film,coating, drying and temporary burning were repeated three times tofabricate a 1 μm-PBNZT thick film sample in which a ferroelectricmaterial film having thickness 1 μm including 4 layers was formed.

Furthermore, in the same way as above, a 1.5 μm-PBNZT thick film sample,in which a ferroelectric material film having thickness 1.5 μm including6 layers was formed, was fabricated, a 2 μm-PBNZT thick film sample, inwhich a ferroelectric material film having thickness 2 μm including 8layers was formed, was fabricated, a 3 μm-PBNZT thick film sample, inwhich a ferroelectric material film having thickness 3 μm including 12layers was formed, was fabricated, a 4 μm-PBNZT thick film sample, inwhich a ferroelectric material film having thickness 4 μm including 16layers was formed, was fabricated, and a 5 μm-PBNZT thick film sample,in which a ferroelectric material film having thickness 5 μm including20 layers was formed, was fabricated.

Next, by subjecting the ferroelectric material film to a heat treatmentby pressurized RTA, the ferroelectric material film is crystallized toform the ferroelectric film. At this time, the heat treatment conditionwas a temperature increase rate 100° C./sec in a pressurized oxygenatmosphere having an oxygen partial pressure of 9.9 atm, whichinstantaneously increased the temperature up to 650° C. and held thetemperature of 650° C. for 1 minute, thereby crystallizing theferroelectric material film. Furthermore, the samples were alsofabricated, in which the crystallization was performed by change of theholding times to 1.5 minutes, 2 minutes, 3 minutes, 4 minutes and 5minutes, respectively.

FIG. 7A is a photograph showing the 5 μm-PBNZT thick film 4-inch wafersample, and FIG. 7B is a photograph showing the 1.5 μm-PBNZT thick film6-inch wafer sample.

In FIG. 8, the drawing denoted by “newly-developed” is a TEMcross-sectional image of a 2 μm-PBNZT thick film, and the drawingdenoted by “conventional product” is a TEM cross-sectional image of thePZT film (FIG. 3A) in Comparative Example relative to Example 1.

It can be seen that air bubbles has entered into the conventionalproduct in FIG. 8, which has poor film quality. In contrast, it can beseen that the ferroelectric film shown by “newly-developed” shown inFIG. 8 has a pillar shape crystal structure or a columnar crystalstructure, and, in spite of a thick film having thickness 2 μm, containsalmost no bubble to give a very good film quality.

FIG. 9A is a drawing showing a SEM cross-sectional image of the 1μm-PBNZT thick film, FIG. 9B is a drawing showing a SEM cross-sectionalimage of the 1.5 μm-PBNZT thick film, FIG. 9C is a drawing showing a SEMcross-sectional image of the 2 μm-PBNZT thick film, FIG. 9D is a drawingshowing a SEM cross-sectional image of the 3 μm-PBNZT thick film, FIG.9E is a drawing showing a SEM cross-sectional image of the 4 μm-PBNZTthick film, and FIG. 9F is a drawing showing a SEM cross-sectional imageof the 5 μm-PBNZT thick film.

FIG. 10A is a drawing showing a result of performing the hysteresisevaluation of the 3 μm-PBNZT thick film, FIG. 10B is a drawing showing aresult of performing the hysteresis evaluation of the 4 μm-PBNZT thickfilm, and FIG. 10C is a drawing showing a result of performing thehysteresis evaluation of the 5 μm-PBNZT thick film.

As shown in FIGS. 10A to 10C, it was confirmed that the ferroelectricfilm of the present invention has an excellent hysteresis property.

Evaluation results of the property of the PBNZT thick film of theExample were as follows. From the results, it was confirmed thatproperties of the PBNZT thick film of the Example are extremelyexcellent even when they are compared with properties of the 3μm-Pb(Zr_(0.52)Ti_(0.48))O₃.

[1] Evaluation Results

d33=470 pm/V

d31=148 pm/V

Poisson's ratio=0.31

tan δ≤0.01

Tc 350° C.

Meanwhile, the d constant is the coefficient representing the degree ofdisplacement when a electric field (V/m) is applied to a piezoelectricmaterial. “d” means the d of Displacement. Depending on the relationbetween the electric field direction and the displacement direction, itis represented by d33, d31 [unit: m/V, C/N] or the like. Usually, theaxis having been subjected to a polarization treatment is represented as3, other axes are represented as 1, 2, and independent d constants inceramics having been subjected to a polarization treatment arerepresented as d31, d33. That is, d33 means a mechanical displacementproportion per the electric field in the 33 direction, and d31 means amechanical displacement proportion per the electric field in the 31direction. When an alternating electric field E is applied to adielectric substance, actually, a part of the electric energy is lost asheat. As a scale showing the loss, generally, the dielectric loss (tanδ) is employed. The dielectric loss is occasionally expressed as adielectric loss coefficient or “tangent of the dielectric loss.” Here, δshows the delay of phase of electric polarization relative to thealternating electric field, that is, means the loss angle. Actually, tanδ is used as a rough estimate showing the quality of a dielectricsubstance, and, generally, it is possible to think that heat generationof a condenser is suppressed when the value is small. Usually, it isexpressed as a form of tan δ=0.03, or 3%.

Example 3

A raw material solution for forming a PBNZT ferroelectric film having pH6.5, viscosity of 40 cps and a contact angle 10° relative to Pt wasfabricated by adding raw material liquids as a formula below.[{(25 mol % PZT sol-gel solution (solvent: ethanol, surplus lead 25%)+5mol % niobium octylate+5 mol % bismuth octylate+3 mol % manganeseoctylate+15 mol % dimethyl succinate)+½ volume 2n butoxy ethanol}+⅛volume (lauric acid 45%+myristic acid 18%+palmitic acid 10%+caprylicacid 8%+oleic acid 8%+capric acid 7%+stearic acid 2%+linoleic acid 2%)+⅛volume ethylmethyl ether]+⅕ volume dimethylaminoethanol  (formula)

Next, in the same way as in Example 1, a 4-inch or 6-inch Si waferhaving a (111)-oriented Pt film formed on the surface is prepared, andthe above-mentioned raw material solution for forming PBNZTferroelectric film is coated on the Si wafer covered with the Ptelectrode by a spin-coating method. Consequently, on the Si wafer, afirst layer coated film is formed. In detail, the solution 1.5 cc forthe 4-inch wafer was coated, the rotation speed of the coated wafer isincreased from 0 to 500 rpm in 3 seconds, the rotation speed of 500 rpmwas held for 5 seconds, then the coated wafer was rotated at 1000 rpmfor 90 seconds and at 3000 rpm for 30 seconds, and the rotation wasstopped.

Next, the first layer coated film was heated and dried at a temperatureof 250° C. for 30 seconds by a hot plate, and, after that, was subjectedto temporary burning at a temperature of 450° C. for 30 seconds.Consequently, on the Si wafer, a first layer ferroelectric substancematerial amorphous film was formed.

Subsequently, in the same way as in the first layer coated film,coating, drying and temporary burning were repeated five times tofabricate a 1 μm-PBNZT thick film sample in which a ferroelectricmaterial film having thickness 1 μm including 6 layers was formed.

Next, by subjecting the ferroelectric material film to a heat treatmentby pressurized RTA, the ferroelectric material film is crystallized toform the ferroelectric film. At this time, the heat treatment conditionwas a temperature increase rate 100° C./sec in a pressurized oxygenatmosphere having an oxygen partial pressure of 9.9 atm, whichinstantaneously increased the temperature up to 650° C. and held thetemperature of 650° C. for 1 minute, thereby crystallizing theferroelectric material film. Furthermore, the samples were alsofabricated, in which the oxygen partial pressure was changed to 5 atmand 7.5 atm, respectively.

FIGS. 11A to 11C are drawings showing results of evaluating thecrystallinity of the PBNZT thick film of the Example by XRD diffraction.

FIG. 11A shows the result of the sample on which the crystallization wasperformed in a pressurized oxygen atmosphere having an oxygen partialpressure of 9.9 atm, and it was confirmed that, in the sample, theorientation can be controlled to (001). FIG. 11B shows the result of thesample on which the crystallization was performed in a pressurizedoxygen atmosphere having an oxygen partial pressure of 5 atm, and it wasconfirmed that, in the sample, the orientation can be controlled to(110). FIG. 11C shows the result of the sample on which thecrystallization was performed in a pressurized oxygen atmosphere havingan oxygen partial pressure of 7.5 atm, and it was confirmed that, in thesample, the orientation can be controlled to (111).

From the results shown in FIGS. 11A to 11C, it is known that theorientation can be controlled depending on the oxygen partial pressurein crystallization even on a Pt (111) substrate, and it becomes possibleto obtain optimum properties by controlling the orientation for everydevice to which the PBNZT thick film is applied.

FIG. 12 is a schematic view showing the crystal of PBNZT thick filmsoriented to (001), (111), (110), respectively. As shown in FIG. 12, itis known that the number of oxygen per the crystal of the PBNZT thickfilm crystallized at an oxygen partial pressure of 9.9 atm to beoriented to (001) is 2, that the number of oxygen per the crystal of thePBNZT thick film crystallized at an oxygen partial pressure of 7.5 atmto be oriented to (111) is 1.5, and that the number of oxygen per thecrystal of the PBNZT thick film crystallized at an oxygen partialpressure of 5 atm to be oriented to (110) is 1.

FIG. 11D is a drawing showing a result of performing hysteresisevaluation of the PBNZT thick film in FIG. 11A, FIG. 11E is a drawingshowing a result of performing hysteresis evaluation of the PBNZT thickfilm in FIG. 11B, and FIG. 11F is a drawing showing a result ofperforming hysteresis evaluation of the PBNZT thick film in FIG. 11C.

As shown in FIGS. 11D to 11F, it was confirmed that the ferroelectricfilm of the present invention has an excellent hysteresis property.

The invention claimed is:
 1. A sol-gel solution for forming a PBNZT ferroelectric film on a substrate, wherein said sol-gel solution comprises a raw material solution comprising a hydrolysis polycondensation reaction product of an alkoxide raw material, and has a contact angle of 1 to not more than 40° with respect to the substrate, wherein the alkoxide raw material comprises Pb, Bi, Nb, Zr and Ti.
 2. The sol-gel solution according to claim 1, wherein said contact angle with respect to the substrate is 1 to not more than 20°.
 3. The sol-gel solution according to claim 1, wherein said sol-gel solution includes a polycarboxylic acid or a polycarboxylic acid ester in the solvent.
 4. The sol-gel solution according to claim 3, wherein said polycarboxylic acid ester includes heteropolyacid ions.
 5. The sol-gel solution according to claim 4, wherein said heteropolyacid ion has a Keggin type structure of the Formula: [XM_(y)M′_(12−y)O₄₀]^(n−), where X is a hetero atom, M is a polyatom, M′ is a polyatom different from M, n is a valence number, and y=1 to
 11. 6. The sol-gel solution according to claim 4, wherein said heteropolyacid ion has a Keggin type structure of the Formula: [XM₁₁O₃₉]^(n−), where X is a hetero atom, M is a polyatom, and n is a valence number.
 7. The sol-gel solution according to claim 4, wherein said heteropolyacid ion has a Keggin type structure of the Formula: [XM_(z)M′_(11−z)O₃₉]^(n−), where X is a hetero atom, M is a polyatom, M′ is a polyatom different from M, n is a valence number, and z=1 to
 10. 8. The sol-gel solution according to claim 4, wherein the sol-gel solution includes, among said heteropolyacid ions, heteropolyacid ions in which the hetero atom includes the group consisting of B, Si, P, S, Ge, As, Mn, Fe and Co, and the polyatom includes the group consisting of Mo, V, W, Ti, Al, Nb and Ta, as a part of a precursor structure of a ferroelectric ceramics.
 9. The sol-gel solution according to claim 1, wherein the sol-gel solution includes at least one of a high viscosity polyhydric alcohol, glycol ethers, a lower alcohol or a basic alcohol in the solvent.
 10. The sol-gel solution according to claim 1, wherein: said PBNZT ferroelectric film includes a perovskite-structured ferroelectric substance of the Formula: (Pb_(1−X)Bi_(X))((TiZr)_(1−Y)Nb_(Y))O₃, wherein X is 1 to 10 mol %; Y is 1 to 10 mol %; and the surplus lead addition amount included in said raw material solution is 15 mol % or more.
 11. The sol-gel solution according to claim 1, wherein said sol-gel solution includes polar solvents.
 12. The sol-gel solution according to claim 11, wherein said polar solvent is any one of methyl ethyl ketone, 1,4-dioxane, 1,2-dimethoxyethane acetamide, N-methyl-2-pyrrolidone, acetonitrile, dichloromethane, nitromethane, trichloromethane, dimethylformamide, monomethylformamide, or combinations thereof.
 13. The sol-gel solution according to claim 2, wherein said sol-gel solution includes an unsaturated fatty acid, wherein: said unsaturated fatty acid is any one of monounsaturated fatty acid, diunsaturated fatty acid, triunsaturated fatty acid, tetraunsaturated fatty acid, pentaunsaturated fatty acid, hexaunsaturated fatty acid, or combinations thereof; said monounsaturated fatty acid is any one of crotonic acid, myristoleic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, eicosenoic acid, erucic acid, nervonic acid, or combinations thereof; said diunsaturated fatty acid is any one of linoleic acid, eicosadienoic acid, docosadienoic acid, or combinations thereof; said triunsaturated fatty acid is any one of linolenic acid, pinolenic acid, eleostearic acid, mead acid, dihomo-γ-linolenic acid, eicosatrienoic acid, or combinations thereof; said tetraunsaturated fatty acid is any one of stearidonic acid, arachidonic acid, eicosatetraenoic acid, adrenic acid, or combinations thereof; said pentaunsaturated fatty acid is any one of bosseopentaenoic acid, eicosapentaenoic acid, osbond acid, clupanodonic acid, tetracosapentaenoic acid, or combinations thereof; and said hexaunsaturated fatty acid is any one of docosahexaenoic acid, nisinic acid, or combinations thereof.
 14. A method for producing a ferroelectric film, wherein the sol-gel solution according to claim 1 is used for production of a PBNZT ferroelectric film that is a ferroelectric film comprising a perovskite-structured ferroelectric substance represented by ABO₃, wherein: said perovskite-structured ferroelectric substance is a PZT-based ferroelectric substance containing Pb²⁺ as A-site ions and containing Zr⁴⁺ and Ti⁴⁺ as B-site ions; the A-site contains Bi³⁺ as A-site compensation ions; the B-site contains Nb⁵⁺ as B-site compensation ions; the content of said A-site compensation ions is 5 to 10 mol % relative to the stoichiometric composition of said perovskite-structured ferroelectric substance; and the content of said B-site compensation ions is 5 to 10 mol % relative to the stoichiometric composition of said perovskite-structured ferroelectric substance.
 15. A method for producing a ferroelectric film, wherein the sol-gel solution according to claim 1 is used for production of a ferroelectric film having a relative permittivity of 400 or more.
 16. A film forming method, comprising the steps of: coating the sol-gel solution according to claim 1 on a substrate to form a coated film on said substrate; temporarily burning said coated film; and repeating the formation of said coated film and said temporary burning a plurality of times to form a ferroelectric material film including a plurality of coated films on said substrate.
 17. The film forming method according to claim 16, wherein: said ferroelectric material film has a thickness of more than 300 nm; and said ferroelectric material film is subjected to a heat treatment to crystallize collectively said ferroelectric material film.
 18. A method for producing a ferroelectric film comprising the steps of: forming a ferroelectric material film on a substrate by using the film forming method according to claim 16; and heat-treating said ferroelectric material film to form a ferroelectric film including a perovskite-structured ferroelectric substance obtained by crystallizing said ferroelectric material film, wherein said ferroelectric film is a PBNZT ferroelectric film that is a ferroelectric film comprising a perovskite-structured ferroelectric substance represented by ABO₃, wherein: said perovskite-structured ferroelectric substance is a PZT-based ferroelectric substance containing Pb²⁺ as A-site ions and containing Zr⁴⁺ and Ti⁴⁺ as B-site ions; the A-site contains Bi³⁺ as A-site compensation ions; the B-site contains Nb⁵⁺ as B-site compensation ions; the content of said A-site compensation ions is 5 to 10 mol % relative to the stoichiometric composition of said perovskite-structured ferroelectric substance; and the content of said B-site compensation ions is 5 to 10 mol % relative to the stoichiometric composition of said perovskite-structured ferroelectric substance.
 19. A method for producing a ferroelectric film comprising the steps of: forming a ferroelectric material film on a substrate, by using the film forming method according to claim 16; and heat-treating said ferroelectric material film to form, on the substrate, a ferroelectric film having a relative permittivity of 400 or more obtained by crystallizing said ferroelectric material film.
 20. The method for producing a ferroelectric film according to claim 17, wherein, when a ferroelectric material film is formed on said substrate, the formation of said coated film and said temporary burning are repeated a plurality of times to form a ferroelectric material film including the plurality of coated films on said substrate.
 21. The method for producing a ferroelectric film according to claim 18, wherein the surface of said substrate has a (111)-oriented Pt or Ir film. 